A. Field of the Invention
The embodiments of the present invention relate to a normally solid polyalkylene carbonate resin, and more particularly, the embodiments of the present invention relate to a method of stabilizing a normally solid polyalkylene carbonate resin against thermal and hydrolytic decomposition for at least producing tough coatings with excellent adhesion to both ferrous and non-ferrous metals.
B. Description of the Prior Art
Poly(alkylene carbonates) are coploymers of carbon dioxide and 1,2-epoxides. They are easily prepared by reacting an aliphatic or epoxide, e.g., ethylene oxide, propylene oxide, isobutylene oxide, in a solvent under pressure of 100 to 700 psig of carbon dioxide using an organometallic catalyst, typically zinc carboxylate, for up to 40 hours at 25° C. to 110° C.
These polymers can also be prepared by reacting a diol having at least 4 carbons separating the hydroxyl groups with a diester of carbonic acid in the presence of a catalyst selected from tertiary amines, alklyammonium salts, pyridinium salts, and basic ion-exchange resins containing active alkylammonium or tertiary amino groups. The end groups are either hydroxyls or carbonate esters.
According to Stevens (in U.S. Pat. Nos. 3,248,414; 3,248,415 and 3,248,416, poly(alkylene carbonate) polyols are prepared by reacting (a) carbon dioxide and 1,2-epoxides; (b) cyclic carbonates, such as ethylene carbonate; or (c) cyclic carbonates and 1,2-epoxide. A minor amount of a polyol is used as an initiator.
U.S. Pat. No. 3,248,415 to Stevens discloses that certain polyamines can be used as initiators in reactions with alkylene carbonates or alkylene oxides and carbon dioxide. These polyamines include: other organic compounds having at 2 active hydrogens, usually from 2-4 active hydrogens are used. By active hydrogen is meant a hydrogen linked directly to a nitrogen, sulfur, or oxygen atom, such as is found in hydroxyl, non-tertiary amino, mercapto, carbamate, and carboxyl groups. Each active hydrogen is linked to a different nitrogen, sulfur, or oxygen atom in the compound.
Polyamines, especially diamines in which the amino groups are primary or secondary, are suitable organics containing 2 active hydrogens. Piperazine and like polyamines wherein each of the nitrogens has one hydrogen linked thereto (secondary amino nitrogens) are preferred, according to Stevens.
Residual catalyst fragments in poly(alkylene carbonates) have a detrimental effect on the stability of these polymers by catalyzing depolymerization reactions (“unzipping”). The higher the temperature, the higher the rate of depolymerization. Even the terminal hydroxyl groups adversely affect the stability of these copolymers and stability is improved by reacting the free hydroxyl groups with a hydroxyl reactive phosphorus compound as disclosed by Dixon et al. in U.S. Pat. No. 4,145,525.
Prior in U.S. Pat. No. 4,528,364 it is stated that the presence of alkaline catalysts remaining in polyalkylene carbonate polyols adversely affect the performance and that these fragments must be removed. In addition, water (moisture) has a detrimental effect, hydrolyzing the polyalkylene carbonate.
Poly(propylene carbonate), for example, decomposes to polylene carbonate by an unzipping mechanism and scission of the carbonate linkage via hydrolysis. Unzipping starts at the end of the chain and continues to proceed by producing more cyclic monomer (propylene carbonate) as the length of the chain decreases. This is an equilibrium reaction where depolymerization and subsequent polymerization occur.
The propylene carbonate produced acts as a plasticiser for the polymer and thus the product as received by the customer becomes clumped together. Pellets of Qpac (Empower Materials, Inc., Newark, Del.) polyalkylene carbonate become stuck together and very difficult to separate; similarly, powered product becomes one solid mass. This is why the additional processing described above (removal of catalyst residues and reacting the terminal hydroxyl groups) is required.